1. Field of the Invention
The present invention relates to a printing apparatus and, particularly to a printing apparatus in which a printhead is mounted on a carriage and the printhead prints while reciprocally scanning the carriage.
2. Description of the Related Art
In a printing apparatus configured to allow the user to replace a printhead mounted on a carriage, a poor contact between the electric contact of the printhead and the electric contact of the carriage that occurs when the user replaces the printhead has not completely been solved in practice though electric contacts have been improved.
The poor contact occurs when small dust is sandwiched between the electric contact of the printhead and that of the carriage upon replacing the printhead. Since this problem arises in the apparatus environment, it is difficult to solve this problem regardless of the improvement of the product. As a practical countermeasure to deal with the poor contact, a contact detection function may be arranged. When a poor contact is detected by contact detection, the user is notified of a message to this detection and prompted to mount the printhead again. The contact detection uses the same voltage as a voltage used in normal printing or a voltage close to it.
There is also a problem that, as the printhead is used for a long period, a circuit in the printhead goes wrong due to aging of the printhead, and a current leaks from the head voltage supply line, causing poor printing. To detect the leakage, a leakage detection function may be arranged. A poor printhead is detected by leakage detection, and the user is notified of a message to this detection and prompted to replace the printhead. Poor printing can therefore be prevented. Conventional leakage detection adopts an arrangement in which power used in normal printing and power used in leakage detection are supplied via the same line, as disclosed in, for example, Japanese Patent No. 2,930,918.
However, the conventional leakage detection uses the same power supply as that used in normal printing. Performing this detection requires time to accumulate charges in a large-capacity capacitor arranged to stabilize a voltage similarly to normal printing. For this reason, leakage detection takes time.
In the conventional arrangement in which the capacitor for stabilizing a head voltage is interposed between the printhead and GND, contact detection also requires a long time. To meet requests for higher resolutions and higher speeds of printing, many printing elements and many printing element arrays are arranged on the circuit substrate of a recent printhead. As a result, several tens to hundred electric contacts are arranged. In the conventional arrangement in which contact detection of one electric contact takes time, it is not even practical to implement contact detection in the apparatus. However, as the number of electric contacts which electrically connect the carriage and the printhead increases, the ratio of poor connections increases. Hence, it is highly desirable to implement contact detection.
Since contact detection of the printhead is a necessary function, to implement contact detection in a printing apparatus, increasing the process speed is an urgent matter. Also, leakage detection requires a high process speed.
In the conventional leakage detection arrangement, a normal head voltage or a voltage close to it is applied in leakage detection. If this arrangement is simply applied to contact detection, the printhead may be damaged in poor mounting of the printhead.